Incompatibility in Plants

Abstract

Its Genetical and Physiological Synthesis SEXUAL reproduction is essentially the formation of a new individual resulting from the fusion of two gametic nuclei. Any hindrance to this fusion, within the regular mating group, except when it is due to a defect in the nuclei themselves, is said to be due to incompatibility. In many fungi the cells carrying the nuclei are undifferentiated: they are hyphal cells which, when growing together, fuse and transfer nuclei from one to another. In flowering plants, the cells containing the nuclei are differentiated into the male pollen grain and the female egg-cell. The pollen grain is carried to the stigma by wind or insects, and in this position it produces a pollen tube which grows down the style, penetrates the egg-cell and discharges the male nuclei, so that they can fuse with their female partners. Breeding experiments have shown that incompatibility is: (1) always genetically determined, and (2) that it acts to prevent the fusion of nuclei from closely related parents. It is a limiting mechanism which takes many forms both genetically and physiologically. An examination of the meaning and relationship of these forms not only gives a clue to their evolution but also to the action of the genes controlling them.